The present invention relates to an electronic circuit and, more particularly, to a battery charging circuit for an electronic apparatus.
Some electronic apparatus are of the type in which a secondary battery and an AC adapter that is connectable to a commercial power source are both provided. When the electronic apparatus is hand carried, the secondary battery is used as a power source. When a commercial power source is available, the AC adapter is used to power the device. After the secondary battery has been completely discharged, the AC adapter is used to charge the secondary battery. The secondary battery may be removed from the electronic apparatus tocharge it by means of an external specific charger.
A trickle charge mode is referred to as the mode in which the secondary battery is recharged while the electronic apparatus is in operation powered by the A.C. adapter that is coupled to the apparatus. This charging mode is a continuous charging of the secondary battery at a low rate for a long time. If in the trickle mode while the electronic apparatus is not in operation, the charging time will not be shortened.
In the conventional trickle charge mode, an overcurrent may flow for discharging, depending on the discharging condition of the secondary battery, so that no current can flow into a load. Further, an overload may be caused on the AC adapter that thereby damages the AC adapter. To prevent damage to the AC adapter, the adapter should have a greater current capacity. Increasing the current capacity results in a loss of the compactness of the electronic apparatus. Instead of increasing the current capacity of the AC adapter, an overcurrent preventing means may be incorporated. Such an overcurrent preventing means may develop problems in that it may be operated in a condition such that, when the discharging current of the secondary battery is great, the current to be applied to the load is less than the normal condition.